apache/iceberg · error · java.lang.UnsupportedOperationException

Cannot convert unknown type to Flink:

Error message

Cannot convert unknown type to Flink: 

What it means

TypeToFlinkType.toFlinkType's primitive() branch hit an Iceberg primitive type it has no Flink logical-type mapping for, so it throws UnsupportedOperationException. This guards against silent mis-typed schemas when bridging Iceberg to Flink types.

Source

Thrown at flink/v2.3/flink/src/main/java/org/apache/iceberg/flink/TypeToFlinkType.java:148

        } else {
          // NANOS
          return new TimestampType(9);
        }
      case STRING:
        return new VarCharType(VarCharType.MAX_LENGTH);
      case UUID:
        // UUID length is 16
        return new BinaryType(16);
      case FIXED:
        Types.FixedType fixedType = (Types.FixedType) primitive;
        return new BinaryType(fixedType.length());
      case BINARY:
        return new VarBinaryType(VarBinaryType.MAX_LENGTH);
      case DECIMAL:
        Types.DecimalType decimal = (Types.DecimalType) primitive;
        return new DecimalType(decimal.precision(), decimal.scale());
      default:
        throw new UnsupportedOperationException(
            "Cannot convert unknown type to Flink: " + primitive);
    }
  }
}

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Upgrade the iceberg-flink runtime to a version whose TypeToFlinkType supports the type.
2. Inspect the table schema and remove/replace the unsupported primitive type.
3. If a newly supported type is missing, patch the switch to add a mapping.

if (type.isPrimitiveType() && !SUPPORTED.contains(type.asPrimitiveType().typeId())) {
  throw new IllegalArgumentException("Unsupported Iceberg type for Flink: " + type);
}

try { flinkType = TypeToFlinkType.toFlinkType(type); } catch (UnsupportedOperationException e) { /* handle unsupported type */ }

When it happens

Trigger: Converting an Iceberg schema containing a primitive type not covered by the switch (e.g. very new/unknown primitive added by a newer Iceberg version, or a null/invalid type reaching the converter).

Common situations: Version skew: table written by newer Iceberg with types this Flink build's converter doesn't know; programmatically constructed malformed Type objects.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Cannot convert unknown type to Flink: ${primitive}
• Invalid primary key '%s'. A primary key must not contain dup
• Invalid primary key '%s'. Column '%s' does not exist.
• Invalid primary key '%s'. Column '%s' is not a physical colu
• Invalid primary key '%s'. Column '%s' is nullable.

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/2d1bda3397e26814. Report an issue: GitHub.